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Due to the high power density, short axial size, and wide permanent magnet (PM) flux linkage regulation range, an axial-flux PM memory machine (AFPMMM) with hybrid Halbach array is investigated in this article. To solve the problem of magnetic density variation of Halbach array composed of different types of PMs in asymmetric bilateral air-gap structure, the analytical method for calculating the air-gap flux density of AFPMMM is presented through mathematical analysis, which uses cylindrical coordinate system instead of Cartesian coordinate system and is solved by equivalent method, separated variable method, and boundary conditions. The magnetic field generated by the Halbach array is divided into three directions: radial, circumferential, and axial. The analytical model is compared with the finite element method (FEM) simulation results to verify its effectiveness. In addition, an approximate piecewise linear hysteresis model with parallelogram return line is established based on the analytical expression of magnetic field. By applying different pulse currents to change the residual flux density of PM, the flux regulation characteristics of the motor are studied, and it is found that the air-gap flux density of the motor can be smoothly adjusted by continuously changing the pulse current, which plays a positive role in solving the problem of online magnetic regulation of the motor. [ABSTRACT FROM AUTHOR]

The induction welding of a stringer on an aircraft fuselage skin with a lightning strike protection (LSP) on the underside of the skin is considered. The presence of LSP makes electromagnetic welding very difficult because it concentrates most of the power induced and is therefore more strongly heated than the stringer–skin interface. A new technic coupled with numerical approach that consists in inserting an electrically conductive material into the tooling in order to modify the magnetic field distribution and limit the power induced in the LSP is presented. A strongly coupled electrothermal 2-D finite element analysis (FEA) is developed to optimize the temperature profile. The 3-D FEA is then carried out in order to validate the optimum design. [ABSTRACT FROM AUTHOR]

This article presents the optimal design of a permanent magnet synchronous generator (PMSG). A finite element (FE) model is used to construct a metamodel, which afterward is utilized to define the objective function that models the PMSG. Kriging modeling is employed along with the design of experiments based on Latin hypercube sampling. The utilization of a surrogate model allows to speed up the optimization process while keeping the accuracy since they are developed from the FE analysis. On the other hand, it has been reported that the non-sorting genetic algorithm (NSGA) III is better than NSGA-II because it can solve multi- and many-objective optimization problems. This article demonstrates by numerical experiments that NSGA-III can be successfully used in the optimal design of PMSG with three objectives. [ABSTRACT FROM AUTHOR]

Strongly coupled electromagnetic–mechanical (ME) problems are presently very relevant for academic research and industrial technology and product development. Although the algorithm basis for such coupled simulations is rather extensive and available in numerous publications, verification of the obtained results is very difficult and relies mainly on expensive, tedious, and time-consuming measurements. The main reason for this is an evident deficiency of reference examples with analytical solutions (ASs) in the available literature. To mitigate the problem, this article defines two strongly coupled electromagnetic–ME problems and presents their AS in detail. The obtained ASs were cross-validated by comparing them against an in-house developed multiphysics finite element method (FEM) solver and an excellent agreement between the two was found. [ABSTRACT FROM AUTHOR]

Soft magnetic composites (SMCs) demonstrate excellent potentials for electromagnetic applications. Isotropy is one critical feature in designing the composite. This work presents a shape optimization algorithm for SMCs subject to isotropy and volume constraints. The maximal isotropic effective permeability is the design target for a fixed volume fraction of the SMCs’ inclusion. Augmented Lagrange is applied to satisfy the volume requirement. In addition, an adaptive weighted sum approach is used to deal with the isotropy constraint. A level-set function is defined on the whole design domain and propagates the shape of the inclusion. Shape derivative is deduced to determine the descent direction. A numerical application is implemented for SMCs in magnetostatics in 2-D for various initial shapes. The local minimum is located at a rapid convergence rate. [ABSTRACT FROM AUTHOR]

Large low-speed drives are designed with a high number of pole pairs, annular and magnetically saturated at rated operation. Large bore diameters tend to unwanted deformations of circular air gap (AG) circumference due to magnetic forces or gravitational forces. The electromagnetic computation with changing geometrical conditions therefore poses a cumbersome non-linear field problem due to its high amount of degrees of freedom. For an accurate predictive model of machine acoustics and vibrations, the study of these topological impacts on the magnetic AG field is indispensable. Particularly when considering an arbitrary AG deformation, related to additional spatial flux harmonics, the computational chain of the finite element method (FEM) involves adaptations at each stage (pre- and post-processing). The proposed modeling approach is universal and reduces the computational effort significantly using finite element (FE) solutions of symmetrical machine parts with varying AG widths. 2-D FE simulations are performed to study the impact of deformations. The results of the approach are compared with FE solutions of a complete 2-D model with an exemplary deformation for validation. The aim of this work is to study both magnetic AG fields and forces efficiently in an exemplary high-pole wind turbine generator with a deformed AG topology by interpolating and assembling appropriately partial model solutions. [ABSTRACT FROM AUTHOR]

We propose a stable and efficient approach to extract the frequency-dependent parasitic effects of any computer-aided design (CAD) model with the finite element method (FEM). An equivalent circuit (EC) of the parasitics for use in transient circuit simulations is generated by applying vector fitting to the result of a full-wave simulation on the one hand and to a magnetoquasistatic (MQS) simulation result on the other hand. The circuit generated from the magnetoquasistatic results is combined with capacitances computed in an electrostatic (ES) simulation. This separate consideration of resistive and inductive, and capacitive effects ensures stability also at low frequencies by avoiding impedance or scattering matrices that otherwise would become ill-conditioned when approaching the dc point. A comparison of measurement and simulation results for the example of a common mode (CM) choke validates the method. [ABSTRACT FROM AUTHOR]

The striking growth of powerful computing resources allows time-efficient solution of computationally demanding problems. In particular, advances in high-performance computing have made stochastic approaches to real-world applications more practical. The belief propagation (BP) algorithm is a probabilistic method typically used in information theory and artificial intelligence. This article exploits the probabilistic message passing attribute of BP for solving stochastic linear systems that naturally arise from finite element formulation of stochastic partial differential equations (PDEs), establishing an explicit connection between the two fields for the first time. The accuracy of the algorithm is validated by comparison to the well-known Monte Carlo method. [ABSTRACT FROM AUTHOR]

The circumferential and axial widths of permanent magnet (PM) pole and E-shape stator pole of linear rotary motor with interlaced PM poles are very influential to the back electromotive force (EMF) and the flux leakage analysis is complex, which causes difficulty in optimization of the motor structure. One of the key issues in optimization design is to calculate the flux leakage accurately. In this article, the main flux and side flux variation laws of stator pole are derived by analytical method. The flux leakage can be divided into the flux leakage between the PM and the mover, flux leakage on the stator tooth tip, and the flux leakage between the adjacent PM poles and stator pole. The 3-D flux leakage calculation model is built, which is suitable for the calculation of magnetic flux based on different motor operating principles. Then the rotational and rectilinear back EMFs are calculated by analytical method, which are consistent with the results analyzed by 3-D finite element method. [ABSTRACT FROM AUTHOR]

This article discusses the properties of the practical application results of the Coulomb and the “tree-cotree” gauge conditions for problems based on massive finite element 3-D-meshes (up to 12 million tetrahedrons) and with the ${A}$ – ${V}$ formulation of the magnetic potential. The influence of the sort of gauging of the magnetic vector potential on the accuracy of the calculated solution of systems of linear algebraic equations (SLAEs) is shown by the example of magnetostatics and quasi-static (frequency domain) benchmark problems. The study was carried out for the cases of solving problems by iterative methods of the Krylov subspace and by direct methods. Iterative methods have shown the complexity of achieving the required solution accuracy with an increase in the number of finite elements and deterioration of the properties of the SLAE. The analysis of the dependence of the iterative process convergence and the required solution accuracy on the number of elements in the mesh and the type of gauging applied is accomplished. For direct methods for solving SLAEs, an a posteriori estimate of the dependence of the value of the relative forward error on the presence and type of the gauge condition is performed. The possibility and efficiency of using block low-rank (BLR) factorization for solving SLAEs in the presence and absence of gauge conditions are considered. The conditions for using the gauging of the magnetic vector potential are shown, which are suitable for simplifying the process of preparing and solving numerical problems and increasing the accuracy of the calculated values of the magnetic vector potential in the frequency domain. [ABSTRACT FROM AUTHOR]

The size of magnetic components can be reduced with novel designs, but the intricate structures are difficult to make due to the limited sets of conventional magnetic core geometries and materials. Magnetic pastes have the flexibility of forming complicated structures with a pressure-less and low-temperature molding process, and are ideal for making the novel magnetic designs. The conventional approach of developing magnetic pastes involves time-consuming experimental iterations to determine the optimal composition parameters. Instead of relying on the trial-and-error efforts, we explored a computer-aided approach to guiding the magnetic paste development by creating material’s microstructure by discrete element method (DEM) and studying the property by finite element method (FEM). From a starting formula with two different-sized spherical powders, we improved the composition guided by DEM and FEM, and studied the magnetic permeability versus two variables: powder mixing ratio and magnetic volume fraction. The simulated permeability agreed well with the experimental data with an average error of only 10%. With the computer-aided formulation methodology demonstrated in this work, one can develop magnetic pastes with minimum experimental efforts and explore different compositions to meet various magnetic design needs. [ABSTRACT FROM AUTHOR]

The ferrofluid seals are widely used in rotating machinery, including some eccentric rotating machinery. However, few studies were conducted on the performance of ferrofluid seals with eccentric rotating shafts. In order to analyze the effect of eccentricity on the sealing performance quantitatively, a simulation method is presented for eccentric ferrofluid seals in this article. The magnetic-flow coupling model is calculated by the finite element method (FEM). Besides, the 3-D boundary variation in the seal clearance is calculated by the moving mesh method. The simulation result shows the inhomogeneous distributions of magnetic induction intensity, magnetic force, and magnetization pressure. Based on the analysis of weak points, the effect of eccentricity on the sealing performance of the ferrofluid seal is studied. The sealing performance decreases gradually with the increase of eccentricity. [ABSTRACT FROM AUTHOR]

Regularly used in power transformers, grain-oriented (GO) steels are also usually chosen for the manufacturing of the stator cores of hydro generator and turbogenerator. These steels are renowned for their high magnetic performances in the rolling direction (RD) (high permeability and low magnetic losses). Nevertheless, in a turbogenerator where GO steels are employed to reduce the size of the stator core, the magnetic flux flows through several successive directions within the plane of the steel. So, the anisotropic behavior of the GO steel has to be considered in the design step of the related devices in order to improve their energy efficiency as well as their diagnosis based on modeling. In this article, an anisotropic phenomenological iron loss model, quite recently developed, has been studied and successfully implemented in a finite element method (FEM) simulation environment. The implementation has been validated against experimental data achieved on an industrial conventional GO grade typically used in turbogenerators. The results show a good agreement of the computational results with the experiments for both quasi-static and dynamic regimes. [ABSTRACT FROM AUTHOR]

This study deals with the analysis of electro-mechanical characteristic analysis on permanent magnet synchronous machines (PMSMs) for electrically driven tools primarily used in industrial applications. This study compares the noise, vibration, and harshness (NVH) characteristic results generated by fractional pole/slot combinations. The electromagnetic (EM) analysis results of the PMSMs are derived using the finite element method (FEM), and the NVH analysis is performed by applying the EM analysis results. The analysis results and the effects of EM characteristics on the vibration of the PMSMs were analyzed. The effects of EM excitation characteristics on the rotor vibrations in the PMSM were compared and analyzed. [ABSTRACT FROM AUTHOR]

Robustness and reliability of modern synchronous motors require an accurate design of the permanent magnets (PMs) while accounting for the motor operating conditions (demagnetizing field and temperature). In this article, the important attribute of a PM non-linear demagnetization model within a finite element method (FEM) simulation environment is clearly emphasized. To do so, starting from the experimental measurement achieved on an NdFeB PM, a toolbox named “PM-Demag” has been developed. This toolbox manages the PM history and updates the PM $B(H)$ characteristics depending on the temperature and the PM working point. Finally, a relatively straightforward coupling is implemented with an FEM software and applied to a simple study case. The results show local magnetization loss in the PM due to the combination of both the temperature and the demagnetizing field. [ABSTRACT FROM AUTHOR]

Power transformer is the main part of the power grid. After some tests and operations of transformers, a certain residual flux density ($B_{r}$) is left in the iron core due to the ferromagnetic material hysteresis phenomenon. When the transformer is switched on with no load, $B_{r}$ will lead to inrush current. Therefore, research on measuring $B_{r}$ is of great significance for transformer protection. In this article, a $B_{r}$ measurement method based on applied dc voltage is proposed. First, combined with the magnetic circuit and transient circuit analysis, the relationship between $B_{r}$ and the extremum value of the transient current difference is obtained. Then, the finite element method (FEM) is used to calculate the transient current under different $B_{r}$ and test circuit parameters; the suitable test circuit parameters will be determined, and then the empirical formula for calculating $B_{r}$ is obtained. Finally, the experimental results verify the correctness of the simulation analysis. [ABSTRACT FROM AUTHOR]

In this article, a 2-D analytical model is presented for brushless double mechanical port flux-switching permanent magnet machines (BDMPFSPMMs). The BDMPFSPMM is an appropriate candidate to be employed as the electric motor in hybrid electric vehicles (HEVs) due to integrating two rotors and two stators into a compact structure. The radial and tangential components of the magnetic flux density are calculated due to permanent magnets and armature currents in each active region of the machine based on the subdomain method. The effects of the saliency on both the rotor and stator structures as well as their interactions are considered. The approach can be used for the magnetic field calculation in BDMPFSPMMs with any combination of rotor- and stator-pole numbers. Based on the computed magnetic flux density, electromagnetic torque, self and mutual inductances, flux linkage, induced voltage, local traction, and unbalanced magnetic force (UMF) are obtained. To validate the proposed model, the analytical results are compared with those obtained from the finite element method (FEM). [ABSTRACT FROM AUTHOR]

Axial flux permanent magnet synchronous motors (AFPMSMs) have advantages over other motor types in terms of efficiency, vibration, and noise. However, torque ripple is an important problem for axial flux permanent magnet (AFPM) motors. One of the methods recommended as a solution to this problem is the skew operation. The skew can be applied to the magnets or the stator. However, for these motors, this process is mostly applied to magnets because the skew applied to the stator makes it difficult to manufacture. In this article, a solution to the torque ripple of an in-wheel AFPMSM for the electric vehicle is sought. For this purpose, designs, optimization, and 3-D analyzes have been carried out. This solution has been applied to magnets designed by skewing for ease of production. 3-D analyses have been carried out by applying skew of up to 40° with an angle of 5° to the magnets in the rotor. In light of the analysis, the most appropriate skew angle that does not affect motor performance has been determined. As a result of the analysis of the motor model obtained with the determined skew angle, it is observed that the torque ripple decreased by 86.71%. Finally, production has been carried out according to the analysis results obtained. [ABSTRACT FROM AUTHOR]

It is important to dimension grounding systems properly, because they protect people and devices. Dimensioning of the grounding system is often made using the finite element method, and the properties of the soil are needed for that. Evolutionary methods can be used for the determination of the parameters of a horizontally layered soil model. The basis for the parameter’s determination is Wenner’s method measurements. In this article, the horizontally layered soil model is analyzed using different soil structures. Different evolutionary methods are tested for the presented problem. The aim of the tests is to determine the most appropriate evolutionary method, between those selected, for the presented problem. [ABSTRACT FROM AUTHOR]

The quality of a local physical quantity obtained by the numerical method, such as the finite element method (FEM), attracts more and more attention in computational electromagnetism. Inspired by the idea of goal-oriented error estimate given for the Laplace problem, this work is devoted to a guaranteed a posteriori error estimate adapted for the quantity of interest (QOI) linked to magnetostatic problems, in particular, to the value of the magnetic flux density. The development is principally based on an equilibrated flux construction, which ensures fully computable estimators without any unknown constant. The main steps of the mathematical development are given in detail with the physical interpretation. An academic example using an analytical solution is considered to illustrate the performance of the approach, and a discussion about different aspects related to the practical point of view is proposed. [ABSTRACT FROM AUTHOR]

In a linear eddy current system excited by a current source, a high-order frequency sensitivity is derived in variational formulation instead of as a discretized state equation. An analytic sensitivity formulation of order n is obtained by sequentially differentiating the variational eddy current system with respect to angular frequency. The high-order frequency sensitivity is implemented through a commercial finite element method. A frequency sensitivity analysis conducted based on two numerical examples verifies the results. [ABSTRACT FROM AUTHOR]

The multiscale finite element method (MSFEM) is a valuable tool to solve the eddy current problem in laminated materials consisting of many iron sheets, which would be prohibitively expensive to resolve in a finite element mesh. It allows using a coarse mesh that does not resolve each sheet and constructs the local fields using predefined micro-shape functions. This article presents for the first time an a posteriori error estimator for the MSFEM, which considers the error with respect to the exact solution. It is based on flux equilibration and a modification of the theorem of Prager and Synge and provides an upper bound for the error that does not include generic constants. Numerical examples show a good performance in both linear and nonlinear cases. [ABSTRACT FROM AUTHOR]

Mathematical modeling and computer simulation of heat transfer in the liver play a key role in prediction of radio frequency ablation outcome. While multi-physics modeling should be used for accurate simulation of heat transfer in a highly perfused organ like the liver, the computational cost of such a problem could have a negative impact on the simulation time. This article extends a highly parallel finite element-based method to simulate the multi-physics heat transfer problem in the liver efficiently. A message passing interface (MPI)-based strong coupling method is developed and tested on cluster nodes. The scalability of this work is assessed by performing simulations on up to 1024 cores. [ABSTRACT FROM AUTHOR]

This article presents a novel surface-mounted permanent magnet motor (SPMM) with hybrid NdFeB-Alnico magnets to achieve low cost and low torque pulsation. Based on the analysis of the effects of stator magnetomotive force (MMF) on rotor magnets, the Alnico magnets can be properly configured to avoid demagnetization. To reduce torque pulsation, three models with different slot-pole combinations are proposed and compared, with the aid of the finite element method (FEM), and the results show that the torque pulsation of the 27-slot/4-pole model is the lowest, which is selected for further optimization. The multi-objective genetic algorithm (MOGA) is adopted to optimize the usage of Alnico and NdFeB magnets, thereby improving torque performance and reducing the cost. To verify the effectiveness of the optimization, the optimized model with hybrid NdFeB-Alnico magnets is compared with other models with only NdFeB magnets under the same operating conditions. As a result, it shows that the optimized model can significantly reduce the cost of magnets while maintaining excellent torque performance. [ABSTRACT FROM AUTHOR]

Soft magnetic composites (SMCs) possess promising electromagnetic characteristics and attract intense research and application interest in the engineering community. Fabrication of composites with customized architecture is feasible due to the recent advances in additive manufacturing techniques. The systematic progress of computational optimization has opened up the possibility of devising such structures. This article aims to optimally design the shape of inclusion in SMCs. Their advantages are potentially high magnetic permeability and low eddy current losses at a certain volume fraction of the iron material. The shape derivative is calculated for the descent direction and the level-set method is used to evolve the domain. We implement the algorithm in 2-D space considering the linear magnetic behavior of iron. In this article, the objective is the effective magnetic permeability at a given volume fraction of inclusion for magnetostatics. [ABSTRACT FROM AUTHOR]

This article presents an effective modeling method for electric machines to reduce the computational cost of finite element (FE) analysis coupled with circuit equations. In this method, center and end regions of the machines are separately modeled. The center of the machines is partially modeled considering their periodic structure. As a result, the total number of elements can be decreased. Moreover, the computational accuracy is kept unchanged by introducing two correction coefficients which adjust the total amount of magnetic flux across the coils. The proposed method is applied to the steady-state characteristic analysis of a turbine generator. It is shown that the proposed method can reduce the computational time to about one-third in comparison with the conventional FE model, while the computational results almost coincide with the measurements. Then, the proposed method is also applied to a time-consuming eddy current analysis of the turbine generator for estimating its transient characteristics. It is shown that the estimated transient constants of the turbine generator are in good agreement with the measured results. [ABSTRACT FROM AUTHOR]

There are some special phenomena like longitudinal end effect, saturation effect, skin effect, edge effect, and half-filled slots which make the single-sided linear induction motor (SSLIM) analysis more complicated compared to its rotary counterparts. Finite element method (FEM) can be the best choice for complete modeling of SSLIM considering all phenomena. But it is not possible to include the non-linear magnetization curve of iron into the time-harmonic FEM analysis. Thus, this article proposes a 2-D time-harmonic FEM considering all phenomena as well as the non-linear magnetization characteristics of iron using appropriate approximation. In order to overcome the Lorentz method calculation error of vertical force caused by inherent discontinuity of magnetic field intensity at the boundaries of elements, a combined Lorentz–Maxwell method is presented. Validity of the methods and final results is proved by comparing the results with analytical results and experimental measurements. [ABSTRACT FROM AUTHOR]

With the continuous improvement of magnetic and mechanical properties of soft magnetic composite (SMC) material, there is a trend to develop novel electrical machines with SMC cores for some special applications. Among these electrical machines, permanent magnet claw pole machine (CPM) has been extensively studied over the past few decades. As linear global winding has been used in this machine, it can be regarded as a linear winding CPM (LWCPM). To improve the performance of LWCPM, a new S-shape winding CPM (SWCPM) is proposed in this article. The main stator structures of the LWCPM and SWCPM are optimized to achieve maximum torque ability. Compared with LWCPM, SWCPM provides higher average torque, power factor, and higher efficiency. The main disadvantage of the proposed SWCPM is its lower flux weakening ability. 3-D finite element model is used to evaluate the performance of the proposed LWCPM and SWCPM. The accuracy of the 3-D finite element model is verified by using a previous prototype. [ABSTRACT FROM AUTHOR]

Accurate models and fast calculations are required for the design of permanent magnet machines. This article presents a 2-D hybrid model for the surface-mounted permanent-magnet synchronous machine (PMSM) combining the Fourier model and the finite element method (FEM). Both magnetic saturation and parallel teeth are taken into account. The model is validated by FEM. The results show that in structures that are saturated, the hybrid model performs much better than the linear Fourier model and simultaneously reduces a large amount of computation compared with FEM. [ABSTRACT FROM AUTHOR]

The flux-concentrating permanent-magnet (FCPM) machine with two V-shape magnet pieces in one stator pole has attracted considerable attention due to its excellent torque density and permanent magnet (PM) usage efficiency, whereas the torque ripple of the FCPM machine is usually high. This article aims to make a multiobjective optimization design for the FCPM machine. The optimization process is divided into three steps for different optimization objectives on two sets of geometric variables at different operation conditions. The simulated results show that the output torque of the optimized FCPM machine is increased significantly while the torque ripple has been decreased greatly. Finally, the open-circuit field distributions, the output torque, the torque-speed characteristics, and PM demagnetization of the optimized FCPM machine are investigated considering different PM shapes and PM temperature rise, which indicates that the optimized FCPM machine has favorable torque characteristics, speed range, and antidemagnetization abilities. [ABSTRACT FROM AUTHOR]

A block-inverse preconditioner (BIP) is proposed to accelerate solving implicit time integration in the context of Newton–Krylov approach used in micromagnetic simulations for solving the Landau–Lifshitz–Gilbert equation. A coefficient matrix is generated and stored for the linear system of Newton method. BIP is formulated by subdividing the coefficient matrix into small blocks and directly inverting them. The cost of preconditioning is low since inverting and multiplying small blocks is fast, which can be further minimized by parallel computing on multicore CPUs or GPUs. The effectiveness, speed, robustness, and scalability of BIP is demonstrated by numerical simulation experiments. Comparisons to incomplete LU preconditioning methods are conducted to demonstrate the effectiveness of BIP. [ABSTRACT FROM AUTHOR]

This paper presents the methodology and validation of high-frequency (HF) transformer simulations, which take into account the frequency dependence of the winding resistances and inductances. The parameters’ frequency dependence is approximated by curve fitting of the values computed by the finite element method (FEM) simulations in the frequency domain. After inverse Fourier transformation into the time domain, the convolution integrals are solved efficiently by the trapezoidal integration rule. The simulation results are validated using measurement data. [ABSTRACT FROM AUTHOR]

In this paper, the modeling process and transient performance analysis for induction heating system (IHS) are carried out, considering the frequency-dependent inductive load. First, the impedance of the inductive load at the frequency range of interest is computed by using the finite element method (FEM). Then the vector fitting (VF) and the passivity enforcement techniques are employed to obtain a stable, causal, and port passive rational approximation model for the considered impedance. Afterward, the circuit synthesis method is used to achieve a circuit representation in terms of the pole-residue rational model. Good agreements between the presented equivalent circuit and the results of the FEM are achieved both on the magnitude and on the phase. Finally, the transient performances of the IHS under the controls of open-loop and closed-loop are conducted. This transient model with the inclusion of frequency-dependent inductive load provides a reliable prediction method of energy efficiency at the early stages of design. [ABSTRACT FROM AUTHOR]

At present, finite element method (FEM) is still the mainstream tool in a range of complex science and engineering applications, including the analysis of structures, heat, fluid, and electromagnetics. However, FEM becomes computationally very intensive when the number of physics equations grows and the mesh is refined. In this paper, we investigated the parallel computing techniques in the nonlinear magnetostatic field solution of an axisymmetrical actuator with permanent magnet by proposing a generalized black-box transmission line method (BB-TLM). A novel black-box circuit model was built to represent complex FEM element data. By means of the transmission line model, each element is isolated and then a series of parallel procedures is considered during the solution stages. The magnetic field distribution and magnetic force of the studied actuator are calculated by the proposed method and the simulation results are compared with COMSOL. Compared with the conventional N-R method, the generalized BB-TLM algorithm greatly reduces the computation time. [ABSTRACT FROM AUTHOR]

This paper investigates the action of eddy current on tank vibration. Sound pressure level (SPL) is measured in situations where the winding is covered with an empty tank and exposed to air to verify the action of eddy current on tank vibration. The results show that tank vibration increases the average SPL by about 23 dB. Through experimental modal analysis, natural frequencies of the winding are away from the 100 Hz excitation but the natural frequency 99.787 Hz of tank is quite close to 100 Hz, which also explains the increase in the SPL. To make simulations on tank vibration caused by eddy current, a 3-D finite-element model is used for analyzing eddy current, electromagnetic (EM) force, as well as tank response in frequency domain. The computation shows a good agreement with the theoretical analysis that the phase angle of the EM force on tank shows a 90° shift compared with that of the winding. Also, the computation simulates the tank vibration caused by eddy current successfully. [ABSTRACT FROM AUTHOR]

This paper presents a method to quickly and accurately deduce the optimal pole-arc coefficient for achieving the maximum suppression of intrinsic shaft voltage in fractional-slot permanent-magnet synchronous machines (FSPMSMs). First, with the aid of the analytical method, not only the pole and slot number combinations which can yield the intrinsic shaft voltage in FSPMSMs but the analytical expression of the intrinsic shaft voltage are derived. Then, the effect of pole-arc coefficient on the intrinsic shaft voltage is investigated, and an optimal pole-arc coefficient which can minimize the intrinsic shaft voltage is calculated. Furthermore, the analytical results are validated by finite element method (FEM) well in 6-pole/9-slot, 8-pole/9-slot, and 8-pole/12-slot FSPMSMs, which indicates that the differences obtained between the optimal pole-arc coefficients by two methods are all less than 10%. In conclusion, considering the rapidity of the analytical method and the precision of the FEM, the analytical method should be used first to deduce an initial value to compress the interval of optimization, then run the calculation iteratively by the FEM to get the exact optimal pole-arc coefficient. [ABSTRACT FROM AUTHOR]

A computational technique is presented in this paper which improves finite element method (FEM) in solving inverse problems. Subregion method is used to select and isolate the area of interest where design parameters for defect shape are updated. An elastic mesh generator is developed in this paper to generate optimal meshes in the selected area to save connectivity matrix until having the most accurate design parameters. Using subregion FEM in solving inverse problems will help in minimizing processing time and memory usage in addition of reducing solution complexity. A 2-D eddy current testing (ECT) problem of detecting and characterizing the location and shape of a defect by separating the defect from entire domain is used to validate the presented subregion FEM algorithm. The elastic mesh generator is investigated to update the preselected design parameters of the defect in each iteration. This meshing technique adds the specialty of using subregion method in inverse problems where elements and nodes numberings are saved inside and outside the defect region. Both the genetic algorithm and simulated annealing optimization techniques are developed to get the accurate defect parameters. The presented subregion FEM results have been verified computationally using conventional FEM. Excellent results of signals agreement and processing time minimization with a factor of 90% with an accuracy of 98% have been achieved. In addition, the presented subregion FEM algorithm has been verified experimentally using aluminum (T6061-T6) and mild steel plate (0.15%–0.30% carbon and Fe) samples. This experiment is carried using an elongated excitation coil in a fixed position mounted on the top of the sample and tunneling magnetoresistive sensor to measure magnetic field. The measured magnetic fields were used as input to the inverse subregion FEM solver and the machined artificial defects were characterized with excellent accuracy. [ABSTRACT FROM AUTHOR]

Based on the base module of Universal Robotics, this paper deals with a 16-pole, 18-slot fractional-slot concentrated-winding permanent magnet synchronous machine (PMSM) for articulated robot applications considering several pole-slot combinations and using an optimum design. The selected PMSM considering the pole-slot combination is optimized and compared both analytically and experimentally. The experimental results confirmed that the proposed PMSM can achieve improved performance at the rated state. Repeatability test results of the proposed smart actuator with a link-attached sphere-mounted retroreflector sensor met the goal of within 100~\mu \textm according to a laser tracker. The analysis results are in good agreement with the experimental results within the maximum 2.5% error in terms of the efficiency. The design, analysis, and experiment with the PMSM for articulated robot applications were conducted successfully. [ABSTRACT FROM AUTHOR]

A rigorous stability analysis of the previously published semi-explicit time domain discontinuous Galerkin (DG) H– $\Phi $ approach for eddy current simulations is presented. The considered DG finite-element method (FEM) enables explicit time stepping in electrically conducting regions and eliminates the need for solving large sparse ill-conditioned equation systems. The considered method utilizes the magnetic scalar potential in electrically non-conducting regions computed by using the nodal finite elements. The theoretical stability limit of the considered semi-explicit time domain approach is obtained by applying the z-transform on the discrete time domain DG-FEM equations and by performing an eigenvalue analysis of the underlying elemental DG-FEM matrices. The obtained results are tested on simple 3-D examples, and an excellent agreement between the theoretical stability limit and the empirically obtained values was found. [ABSTRACT FROM AUTHOR]

This paper proposes an optimal design for a salient pole wound field synchronous machine (WFSM) with a single flux barrier to improve torque performance and obtain a wide operating range, simultaneously. The proposed WFSM motor can effectively decrease q -axis inductance to improve the saliency ratio ( X_{d}/X_{q}) and increase the reluctance torque. To maximize the saliency ratio and improve the torque characteristics, the single flux barrier is optimized, considering the magnetic saturation that uses Kriging method based on Latin hypercube sampling and a genetic algorithm. The 2-D finite element analysis results by the aid of JMAG-Designer shows that the saliency ratio X_{d}/X_{q}$ , the reluctance torque, and the total torque of the optimal model are increased by 9.27%, 20.45%, and 6.17%, respectively, compared with those of the basic model. Finally, the performance of the optimal motor is verified through an experimental test, which indicates good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

The field calculus for electrical machines (EMs) is realized solving subdomain problems. Most often, the latter are solved using either finite element analysis (FEA) or the semi-analytical solution of a Laplace or Poisson equation obtained by separation of variables. The first option can capture complex geometries but becomes slow for high accuracy, whereas the second is fast but limited to simple periodic geometries and linear or infinite permeable materials. This paper presents the 2-D implementation of the spectral element method (SEM) for the modeling of EMs. The polynomial basis functions used to approximate the solution in each domain are reaching exponential convergence similar to the semi-analytical solution. Moreover, each element can be represented by a non-square shape resulting in the possibility to model complex geometries. Following the results in this paper, significantly fewer degrees of freedom are needed for the SEM to achieve the approximation similar to the FEA, and consequently less memory and computational time are required. [ABSTRACT FROM AUTHOR]

In this paper, a novel direct drive, bilateral planar switched reluctance generator (BPSRG) is developed for 2-D wave energy conversion with a mixed type of flux circulation. The proposed BPSRG has longitudinal flux type of the magnetic circuit on one direction and transverse flux-type magnetic circulation for the other perpendicular direction. The characteristics of the magnetic flux and static inductance are calculated for the BPSRG based on the 3-D finite-element method, in order to ensure negligible coupling effect between any phases. Theoretical model of the BPSRG is derived, and parameters that impact the open-loop operation performance of the power generation are analyzed, optimized, and supported by experimental results. [ABSTRACT FROM AUTHOR]

The current capacity of superconducting materials is far larger than that of copper. This paper utilizes MgB2 wires as stator armature windings to obtain a higher output power capacity and presents the electromagnetic design of a direct drive dual-stator superconducting permanent magnet (PM) wind power generator of several megawatts. Considering the irreversible demagnetization in PM materials caused by the huge stator current, several new rotor pole configurations are presented. The features of each configuration are discussed, and the finite element method results show that the output power capacity of the proposed generator can be raised by 8% because the stator current can be larger for the generator with new rotor configurations under the restriction of demagnetization. [ABSTRACT FROM AUTHOR]

This paper proposes a novel magnetic structure of a linear oscillating actuator (LOA). The higher efficient magnetic structure is necessary for reduction in size and weight of an LOA. In a conventional optimization method using a genetic algorithm, it depends on an initial shape hard, and it is difficult to get a novel magnetic structure. In this paper, the topology optimization method which does not need the initial shape is applied to an LOA. The unguessed magnetic structure with magnetization direction and ferromagnetic shape is computed, and the validation of calculated structure is confirmed through the measured results. [ABSTRACT FROM AUTHOR]

A method of getting the more accurate equivalent core length through 3-D electromagnetic finite element method (FEM) (3-D FEM) is presented in this paper. It is a matter of course that 2-D FEM is mostly used to evaluate the rotating machine performance instead of 3-D FEM. It takes 106 times longer to complete 3-D FEM than to complete 2-D FEM according to the simulation data in this paper. The motor has the radial air-cooling ducts in the stator. The use of radial air-cooling ducts has an effect on the electrical performance of its machine due to the fringing effect between ducts. The way to consider that effect is that the actual core length has to be replaced with the equivalent core length to reflect the magnetic circuit of 2-D perspective. However, there is 12% error of the root mean square no-load voltage between 2-D and 3-D FEM in 16 MVA salient pole synchronous motor. The cause of the error is the miscalculated equivalent core length in 2-D FEM. The purpose of this paper is to study the cause of the error through 3-D FEM to get the more accurate equivalent core length in 2-D FEM. Finally, Generator open circuit characteristic test is also carried out to verify the no-load voltage of 2-D and 3-D FEM. [ABSTRACT FROM AUTHOR]

A novel hybrid-flux permanent-magnet (PM) generator, which has both axial flux and radial flux, is proposed. An axial-flux PM generator is designed by a reluctance network method and the 3-D finite element method. Using these results, this paper proposes a radial-flux and hybrid-flux machine, whose main dimensions are chosen to the same values as a commercialized one. The proposed hybrid-flux machine has the largest output power per volume. The power density of the proposed generator is 9.4 times larger than that of the commercialized one. The efficiencies of the proposed hybrid generator and a radial generator are same as each other, and are larger than those of an axial and the commercialized generators. [ABSTRACT FROM AUTHOR]

Non-skewed asymmetrical rotors bars can be used to eliminate the slot harmonic fields and the resulting noise and vibration in cage induction motors. However, it is difficult to determine the spatial distribution of the asymmetrical rotor bars and the slot combinations, which can affect the loss and the air gap force significantly. With a 5.5 kW, 4-pole induction motor as an example, this paper studies the influence of the above factors on the loss and the air gap force by time-stepping finite element method, and the experiments are performed to validate the calculations. [ABSTRACT FROM AUTHOR]

This paper discusses the implementation of the inverse Jiles–Atherton vector hysteresis model with 2-D finite element (FE) method for the analysis of a hysteresis motor electromechanical behavior. A differential reluctivity tensor couples the hysteresis model with the magnetic vector potential-based FE model. Simulation results are validated by experimental data obtained from a specially designed machine. [ABSTRACT FROM AUTHOR]

This paper proposes a coupled analysis method to deal with ion generation and ion drift in the air. Electric discharge is utilized in various products, and it is very important to clarify not only how much ion is generated but also where ion drifts in the air. The proposed method, which modeled interactions between electric field and ion behavior, including ion generation, ion drift, and charging of a dielectric body, has succeeded in calculating charge removal of a metallic target, which was tens of millimeters away from a pin electrode as a source of generated ion. The calculated results show that the amount of generated ion is drastically changed because electric field is affected by electric charge of ion in the air and charging of a dielectric body. This paper also reports a comparison of measured and calculated results of charge removal time of a metallic target, which were found to be in good agreement. [ABSTRACT FROM AUTHOR]

In this paper, dynamic reluctance mesh model (DRM) combined with an improved iron losses prediction model are presented to provide fast and accurate way to evaluate the iron losses for permanent magnet (PM) motors with pulsewidth-modulated power supply. A DRM model for high-speed train PM traction motor is first built. The magnetic field distribution for one cycle is then obtained using the DRM method. An improved engineering model of iron losses prediction is applied. Finally, the simulation and testing results are presented to confirm that the proposed combined method is accurate and effective as the finite element method (FEM) model with much less time consumed. [ABSTRACT FROM AUTHOR]